Adsorbate vibrational effects on the photodesorption of CO from Cu(001)

We have studied the desorption dynamics of vibrationally excited CO on Cu(0 01), induced by femtosecond pulses of visible light. The theory is based on a density matrix approach and the propagation of wave packets using a basi s of two electronic states and a model which includes the distance from CO to the surface, and the displacement corresponding to a frustrated-translat ion mode of the adsorbate vibration. The model incorporates potential energ y surfaces from electronic structure calculations and contains dissipation effects represented by complex potentials. Equations for density amplitudes are solved nonperturbatively with a propagation procedure valid for large light fluence values. The population of vibrational states of the adsorbed CO were calculated versus time as it desorbs. Desorption yields are found t o be more pronounced for initially excited vibrational states. Temperature effects are considered for several initial thermal equilibrium distribution s before the arrival of the light pulse.